Successive image flames contained within a television signal are often almost identical. Images broadcasted in television signals often do not change substantially from frame to frame resulting in a substantial correlation between the information of the two successive frames. Many systems have been devised to take advantage of this correlation by appropriately encoding the image based on predictive schemes to maintain a frame rate of the television signal while reducing the overall number of bits that are required to describe each image frame. Established encoded video signal formats for compression of video data for high definition television include the MPEG-1 and -2 standards described in, for example, U.S. Pat. Nos. 5,293,229 and 5,231,484, which are incorporated by reference herein.
A single encoder circuit possessing adequate processing speed to perform image prediction, such as motion estimation, from frame to frame and to encode each received image frame is very costly to manufacture. In order to minimize video encoder cost, multiple spatially-separated video encoder processors have been used, wherein each encoder performs the motion estimation for specific regions of an image frame and generates corresponding portions of the digital video signal for those regions. For example, four encoder processors have been used to perform motion estimation and generate the corresponding encoded video signal, wherein each encoder processor operates on a respective quadrant of a display partitioned into a matrix of two-by-two quadrants. Other partition arrangements consisting of vertical or horizontal stripes, fixed or moving have been proposed.
All known spatially-separated video encoding techniques share a common problem concerning motion estimation. When an object that appears in a first quadrant is encoded, it may be predicted from any one of the adjacent quadrants' previous frames if the object was in such quadrant and moving toward the first quadrant. As a consequence, picture information from the adjacent quadrants must be made available to the first quadrant encoder processor. Accordingly, picture information for each quadrant must be shared with its neighbor quadrant to provide adequate motion estimation throughout each image frame. Such an information sharing requirement significantly increases hardware and interconnection complexity and cost.
Known methods that avoid the sharing of picture information between quadrants require that motion estimation be constrained within quadrants or not performed at all in quadrant boundary regions. However, such methods cause undesirable visible artifacts in the coded picture. Known video decoders share much of the same problems as encoders.
Therefore, there is a recognized need for low cost video encoder and decoder circuits having reduced hardware and interconnection complexity.